6-O-methylerythromycin A (Clarithromycin) is a semisynthetic macrolide antibiotic of formula ##STR1## which exhibits excellent antibacterial activity against gram-positive bacteria, some gram-negative bacteria, anaerobic bacteria, Mycoplasma, and Chlamidia. It is stable under acidic conditions and is efficacious when administered orally. Clarithromycin is a useful therapy for infections of the upper respiratory tract in children and adults.